Gonadotropin-releasing hormone (GnRH) is the central regulator of the hypothalamic-pituitary-gonadal axis. Accurate expression of GnRH is critical for proper reproductive function as dysregulation of GnRH leads to idiopathic hypogonadotropic hypogonadism (IHH), Kallmann's Syndrome, and infertility. The precise molecular mechanisms involved in the pathogenesis of these reproductive disorders are unclear and com- plex as these diseases exhibit phenotypic and genetic heterogeneity. GnRH gene expression is targeted to a highly specialized, dispersed population of approximately 800 neurons in the hypothalamus. The mechanisms by which GnRH gene expression is restricted to this functionally distinct subset of neurons are not fully understood. The purpose of this proposed research is to investigate the roles of evolutionary conserved, far-upstream regulatory regions of the GnRH gene in neuronal specification and differentiation, with the goal of identifying factors influencing the IHH phenotype.The following aims will address these roles at the levels of transcriptional regulation, in vivo regulation, chromatin structure, and histone modifications. Specific Aim 1: To characterize evolutionarily conserved, far-upstream enhancer regions in neuron-specific expression of the GnRH gene using model GnRH neuronal cell lines. Specific Aim 2: To test the role of the far-upstream enhancer regions of the GnRH gene in targeting GnRH expression to GnRH neurons in vivo in transgenic mice. Specific Aim 3: To determine chromatin structure of GnRH regulatory elements in developmental regulation of GnRH using Chromatin Immunoprecipitation (ChIP) in model GnRH neuronal cell lines. PUBLIC HEALTH RELEVANCE: Idiopathic hypogonadotropic hypogonadism and Kallmann's Syndrome are human reproductive disorders caused by defects in GnRH production and in the development of neurons in the brain that produce GnRH. This research will elucidate mechanisms of the complex genetic and phenotypic heterogeneity of these disorders at the molecular level of transcriptional control of the GnRH gene, through examination of the roles of evolutionarily conserved, far-upstream regulatory elements in the development and function of the GnRH neuron.